This invention relates in general to an apparatus for performing a hydroforming operation on a closed channel workpiece. In particular, this invention relates to an improved structure for such a hydroforming apparatus that is capable of performing two or more hydroforming operations simultaneously to decrease cycle time and increase productivity.
Hydroforming is a well known metal working process that uses pressurized fluid to expand a closed channel workpiece, such as a tubular member, outwardly ir conformance with a die cavity having a desired shape. A typical hydroforming apparatus includes a frame having two die sections that are supported thereon for relative movement between opened and closed positions. The die sections have cooperating recesses formed therein which together define a die cavity having a shape corresponding to a desired final shape for the workpiece. When moved to the opening position, the die sections are spaced apart from one another to allow a workpiece to inserted within or removed from the die cavity. When moved to the closed position the die sections are disposed adjacent to one another so as to enclose the workpiece within the die cavity. Although the die cavity is usually somewhat larger than the workpiece to be hydroformed, movement of the two die sections from the opened position to the closed position may, in some instances, cause some mechanical deformation of the hollow member. In any event, the workpiece is then filled with fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid within the workpiece is increased to such a magnitude that the workpiece is expanded outwardly into conformance with the die cavity. As a result, the workpiece is deformed into the desired final shape. Hydroforming is an advantageous process for forming vehicle frame components and other structures because it can quickly deform a workpiece into a desired complex shape.
In a typical hydroforming apparatus, the two die sections are arranged such that an upper die section is supported on a ram of the apparatus, while a lower die section is supported on a bed of the apparatus. A mechanical or hydraulic actuator is provided for raising the ram and the upper die section upwardly to the opened position relative to the bed and the lower die section, thereby allowing a previously deformed workpiece to be removed from the die cavity and new workpiece to be inserted therein. The actuator also lowers the ram and the upper die section downwardly to the closed position relative to the bed and the lower die section, allowing the hydroforming process to be performed. To maintain the die sections together during the hydroforming process, a mechanical clamping device is usually provided. The mechanical clamping device mechanically engages the die sections (or, alternatively, the ram and the base upon which the die sections are supported) to prevent them from moving apart from one another during the hydroforming process. Such movement would obviously be undesirable because the shape of the die cavity would become distorted, resulting in unacceptable variations in the final shape of the workpiece.
Although known hydroforming apparatuses have been found to function satisfactorily, the use of a single hydroforming die within a single hydroforming apparatus has been found to be somewhat inefficient from a time consumption standpoint. This is because each operational cycle performed by the hydroforming apparatus involves both a preliminary step of filling the article to be hydroformed with the hydroforming fluid prior to performing the hydroforming process, and a subsequent step of emptying the hydroforming fluid from the article after performing the hydroforming process. These filling and emptying steps can consume relatively long periods of time, particularly when the articles to be formed are physically large, as is often the case in the manufacture of vehicle frame components. This inefficiency is further exacerbated when the hydroforming apparatus is used to manufacture products in relatively high volumes, as is also the case in the manufacture of vehicle frame components. Thus, it would be desirable to provide an improved structure for a hydroforming apparatus that is capable of performing two or more hydroforming operations simultaneously to decrease operational cycle time and, therefore, increase overall productivity.